1. Field of the Invention
The present invention relates to a combined cathode and diaphragm unit for the electrolytic cells, and more particularly the present invention relates to such units for electrolytic cells utilized for the electrolysis of sodium chloride.
2. Prior Art
Electrolysis cells utilizing asbestos diaphragms have been known for many years, and considerable commercial production has been achieved utilizing same. Although many efforts have been made to eliminate the use of asbestos as a diaphragm material, the fact remains that asbestos has so many advantages that it is still in widespread use. Efforts to improve chlor-alkali cells utilizing asbestos diaphragms have been made for many years, but improvements are still being found and present invention relates to such an improvement.
It has been well known to combine asbestos fibers with other materials such as bonding agents for a variety of purposes. U.S. Pat. No. 3,723,264 teaches a diaphragm for use in electrochemical oxidation of an olefinic compound. The diaphragm comprises an asbestos being bound with a polymeric binder including tetrafluoroethylene. U.S. Pat. No. 3,694,281 also teaches the use of innumerable binders for the impregnation of the asbestos matrix. U.S. Pat. No. 3,704,221 broadly discloses the bonding of asbestos with fluorohydrocarbons. The reference teaches the use of a fibrous mat formed from asbestos or the like and which is reinforced with the bonding agent, which is preferably a fluorocarbon resin. However, the reference does not appear to directly teach the use of fluorocarbon bonding agents for asbestos diaphragms in chlor-alkali cells. Netherlands Pat. No. 740,587 teaches the bonding of asbestos fibers for use in chlor-alkali diaphragms. Included in the bonding materials are fluorocarbon resins along with a variety of other resins. However, the processing for the binding and preparation of the asbestos diaphragm differs from that utilized in the present invention. Accordingly, although considerable prior art is available on the bonding of asbestos, it is believed that the prior art does not teach applicant's polymer impregnated asbestos processed with a special cathode screen to produce the desired improved results in chlor-alkali cells.
As noted above, U.S. Pat. No. 4,049,841 discloses a cathode having special surface characteristics which may be combined with various fiber diaphragms such as asbestos and provide an improvement in lowering the hydrogen overvoltage of the cathode. Similarly, U.S. Pat. Nos. 3,945,907 and 3,974,058 show special cathodes having a low hydrogen overvoltage. However, it is believed that the advantages achieved by the combined cathode and diaphragm unit of this invention are not suggested by any of these prior art patents.